Method of manufacturing EUV photo masks

ABSTRACT

In a method of manufacturing a photo mask, an etching mask layer having circuit patterns is formed over a target layer of the photo mask to be etched. The photo mask includes a backside conductive layer. The target layer is etched by plasma etching, while preventing active species of plasma from attacking the backside conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application62/738,709, filed Sep. 28, 2018, the entire disclosure of which isincorporated herein by reference.

BACKGROUND

Photolithography operations are one of the key operations in thesemiconductor manufacturing process. Photolithography techniques includeultraviolet lithography, deep ultraviolet lithography, and extremeultraviolet lithography (EUVL). The photomask is an important componentin photolithography operations. It is critical to fabricate EUVphotomasks free of defects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A, 1B, 1C, 1D, 1E, 1F and 1G schematically illustrate a method offabricating an EUV photomask according to an embodiment of thedisclosure.

FIG. 2 shows a schematic view of a hard etching cover according to anembodiment of the present disclosure.

FIG. 3 shows a schematic view of an etching operation using a hardetching cover according to one embodiment of the present disclosure.

FIGS. 4A, 4B, 4C and 4D show schematic views of hard etching coversaccording to embodiments of the present disclosure.

FIGS. 4E and 4F show structures of hard etching covers according toembodiments of the present disclosure.

FIG. 5 shows operations of loading an EUV photo mask to be etched intoan etching chamber through a load lock chamber.

FIG. 6 shows a schematic view of an etching operation of an EUV photomask according to one embodiment of the present disclosure.

FIG. 7 shows a schematic view of an etching operation of an EUV photomask according to another embodiment of the present disclosure.

FIG. 8 shows a schematic view of an etching operation of an EUV photomask according to another embodiment of the present disclosure.

FIGS. 9A, 9B and 9C show view of various cover supports according toembodiments of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

Embodiments of the present disclosure provide a method of manufacturingan EUV photo mask. More specific, the present disclosure providestechniques to prevent or suppress damage on backside conductive layer ofan EUV photo mask.

EUV lithography (EUVL) employs scanners using light in the extremeultraviolet (EUV) region, having a wavelength of about 1 nm to about 100nm, for example, 13.5 nm. The mask is a critical component of an EUVLsystem. Because the optical materials are not transparent to EUVradiation, EUV photo masks are reflective masks. EUV photo masks requirevery low surface roughness and must have no resolvable defects.

An EUV photo mask with circuit patterns for EUV lithography requiresvarious etching operations, such as plasma dry etching. An EUV photomask to be etched is placed on a mask stage in a plasma etching chamber.In some embodiments, the mask stage includes an electric chuck mechanismto hold the EUV photo mask during the plasma etching. In otherembodiments, the EUV photo mask is merely placed on the cathode of themask stage. An EUV photo mask includes a backside conductive layer tothe electric chuck mechanism. However, when a large gap exists betweenthe EUV photo mask and the stage, active species of the plasma maydiffuse to the bottom portion of the EUV photo mask, causing damage onthe backside conductive layer of the EUV photo mask. Damage on thebackside conductive layer may causes various problems, such asgeneration of particles and/or tree-like erosion at the edge of theconductive film. These particles and/or defects in the backsideconductive layer may cause insufficient chucking and/or defects on thecircuit patterns on the front side of the EUV photo mask.

The present disclosure provides techniques to prevent the active speciesof the plasma from entering the side portions and the bottom portion ofthe EUV mask during plasma etching, thereby suppressing damage on thebackside conductive layer of an EUV photo mask caused by active species.

FIGS. 1A-1G schematically illustrate a method of fabricating an EUVphotomask 5 for use in extreme ultraviolet lithography (EUVL). It isunderstood that additional operations can be provided before, during,and after processes shown by FIGS. 1A-1G, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable.

In some embodiments, the EUV photomask with circuit patterns is formedfrom a EUV photo mask blank 5. The EUV photo mask blank 5 includes asubstrate 10, a multilayer Mo/Si stack 15 of multiple alternating layersof silicon and molybdenum, a capping layer 20, an absorber layer 25 anda hard mask layer 30. Further, a backside conductive layer 45 is formedon the backside of the substrate 10, as shown in FIG. 1A.

The substrate 10 is formed of a low thermal expansion material in someembodiments. In some embodiments, the substrate is a low thermalexpansion glass or quartz, such as fused silica or fused quartz. In someembodiments, the low thermal expansion glass substrate transmits lightat visible wavelengths, a portion of the infrared wavelengths near thevisible spectrum (near-infrared), and a portion of the ultravioletwavelengths. In some embodiments, the low thermal expansion glasssubstrate absorbs extreme ultraviolet wavelengths and deep ultravioletwavelengths near the extreme ultraviolet. In some embodiments, the sizeof the substrate 10 is 152 mm×152 mm having a thickness about 20 mm.

In some embodiments, the Mo/Si multilayer stack 15 includes from about30 alternating layers each of silicon and molybdenum to about 60alternating layers each of silicon and molybdenum. In certainembodiments, from about 40 to about 50 alternating layers each ofsilicon and molybdenum are formed. In some embodiments, the silicon andmolybdenum layers are formed by chemical vapor deposition (CVD),plasma-enhanced CVD (PECVD), atomic layer deposition (ALD), physicalvapor deposition (PVD) (sputtering), or any other suitable film formingmethod. Each layer of silicon and molybdenum is about 2 nm to about 10nm thick in some embodiments. In some embodiments, the layers of siliconand molybdenum are about the same thickness. In other embodiments, thelayers of silicon and molybdenum are different thicknesses. In someembodiments, the thickness of each layer of silicon and molybdenum isabout 3 nm to about 4 nm.

The capping layer 20 is disposed over the Mo/Si multilayer 15. In someembodiments, the capping layer 20 is made of ruthenium having athickness of from about 2 nm to about 10 nm. In certain embodiments, thethickness of the capping layer 20 is from about 2 nm to about 4 nm. Insome embodiments, the capping layer 20 is formed by chemical vapordeposition, plasma-enhanced chemical vapor deposition, atomic layerdeposition, physical vapor deposition, or any other suitable filmforming method.

The absorber layer 25 is disposed over the capping layer 20. In someembodiments, the absorber layer 25 is Ta-based material. In someembodiments, the absorber layer 25 is made of TaN and/or TaBN, having athickness from about 25 nm to about 100 nm. In certain embodiments, theabsorber layer 25 thickness ranges from about 50 nm to about 75 nm. Insome embodiments, the absorber layer 25 is formed by chemical vapordeposition, plasma-enhanced chemical vapor deposition, atomic layerdeposition, physical vapor deposition, or any other suitable filmforming method.

In some embodiments, an antireflective layer (not shown) is optionallydisposed over the absorber layer 25. The antireflective layer is made ofa silicon oxide, TaBO, TaO and/or TaON in some embodiments, and has athickness of from about 2 nm to about 20 nm. In some embodiments, thethickness of the antireflective layer is from about 3 nm to about 6 nm.In some embodiments, the antireflective layer is formed by chemicalvapor deposition, plasma-enhanced chemical vapor deposition, atomiclayer deposition, physical vapor deposition, or any other suitable filmforming method.

The hard mask layer 30 is disposed over the absorbing layer 25 in someembodiments. The hard mask layer 30 is formed over the antireflectivelayer in some embodiments where the antireflective layer exists. In someembodiments, the hard mask layer 30 is made of silicon, a silicon-basedcompound, chromium, a chromium-based compound and/or ruthenium having athickness of about 4 nm to about 20 nm. In some embodiments, thechromium-based compound includes CrON, chromium oxide and/or chromiumnitride. In some embodiments, the hard mask layer 30 is formed bychemical vapor deposition, plasma-enhanced chemical vapor deposition,atomic layer deposition, physical vapor deposition, or any othersuitable film forming method.

The backside conductive layer 45 is disposed on a second main surface ofthe substrate 10 opposing a first main surface of the substrate 10 onwhich the Mo/Si multilayer 15 is formed. In some embodiments, thebackside conductive layer 45 is made of chromium, chromium oxide,chromium oxynitride, chromium nitride, TaB or other Ta based conductivematerial.

A thickness of the backside conductive layer 45 is in a range from about10 nm to about 400 nm in some embodiments. In other embodiments, thebackside conductive layer 45 has a thickness of about 20 nm to about 100nm. In certain embodiments, the thickness is in a range from about 65 nmto about 75 nm.

In some embodiments, the backside conductive layer 45 is formed byatmospheric chemical vapor deposition (CVD), low pressure CVD,plasma-enhanced CVD, laser-enhanced CVD, atomic layer deposition (ALD),molecular beam epitaxy (MBE), physical vapor deposition includingthermal deposition, pulsed laser deposition, electron-beam evaporation,ion beam assisted evaporation and sputtering), or any other suitablefilm forming method.

In some embodiments, the area of the backside conductive layer 45 issmaller than the area of the substrate, and a circumference portion ofthe second main surface of the substrate 10 is exposed (not covered bythe backside conductive layer 45) as shown in FIG. 1A. When thesubstrate 10 is a 6-inch substrate, i.e., 152 mm×152 mm, the size of thebackside conductive layer 45 is greater than 142 mm×142 mm and smallerthan 150 mm×150 mm in some embodiments. In other embodiments, the sizeof the backside conductive layer 45 is greater than 144 mm×144 mm andsmaller than 148 mm×148 mm.

In the fabrication of an EUV photo mask 5, a first photoresist layer 35is formed over the hard mask layer 30 of the EUV photo mask blank, andthe photoresist layer 35 is selectively exposed to actinic radiation.Before the first photoresist layer 35 is formed, the EUV photo maskblank is subject to inspection. The selectively exposed firstphotoresist layer 35 is developed to form a pattern 40 in the firstphotoresist layer 35. In some embodiments, the actinic radiation is anelectron beam or an ion beam. In some embodiments, the pattern 40corresponds to a pattern of semiconductor device features for which theEUV photo mask 5 will be used to form in subsequent operations.

Next, the pattern 40 in the first photoresist layer 35 is extended intothe hard mask layer 30 forming a pattern 41 in the hard mask layer 30exposing portions of the absorber layer 25, as shown in FIG. 1B. Thepattern 41 extended into the hard mask layer 30 is formed by etching, insome embodiments, using a suitable wet or dry etchant that is selectiveto the hard mask layer 30. After the pattern 41 by the hard mask layer30 is formed, the first photoresist layer 35 is removed by photoresiststripper to expose the upper surface of the hard mask layer 30, as shownin FIG. 1C.

Then, the pattern 41 in the hard mask layer 30 is extended into theabsorber layer 25 forming a pattern 42 in the absorber layer 25 exposingportions of the capping layer 20, as shown in FIG. 1D. The pattern 42extended into the absorber layer 25 is formed by etching, in someembodiments, using a suitable wet or dry etchant that is selective tothe absorber layer 25. In some embodiments, plasma dry etching is used.

As shown in FIG. 1E, a second photoresist layer 45 is formed over theabsorber layer 25 and filling the pattern 42 in the absorber layer 25.The second photoresist layer 45 is selectively exposed to actinicradiation such as electron beam, UV radiation and/or laser beam. Theselectively exposed second photoresist layer 45 is developed to form apattern 50 in the second photoresist layer 45. The pattern 50corresponds to a black border surrounding the circuit patterns.

Next, the pattern 50 in the second photoresist layer 45 is extended intothe absorber layer 25, capping layer 20, and Mo/Si multilayer 15 forminga pattern 51 in the absorber layer 25, capping layer 20, and Mo/Simultilayer 15 exposing portions of the substrate 10, as shown in FIG.1F. The pattern 51 is formed by etching, in some embodiments, using oneor more suitable wet or dry etchants that are selective to each of thelayers that are etched. In some embodiments, plasma dry etching is used.

Then, the second photoresist layer 45 is removed by a suitablephotoresist stripper to expose the upper surface of the absorber layer25. The pattern 51 in the absorber layer 25, capping layer 20, and theMo/Si multilayer 15 defines a black border of the photomask 5 in someembodiments of the disclosure, as shown in FIG. 1G. After removal of thesecond photoresist layer, the photomask 5 undergoes a cleaningoperation, inspection, and the photomask 5 is repaired as necessary, toprovide a finished photomask 5.

In the present embodiments, in at least one of the plasma dry etchingoperations as set forth above, an etching hard cover 100 is used toprevent the active species of the plasma from entering the side portionsand the bottom portion of the EUV photo mask 5 during plasma etching.

FIG. 2 is a perspective view of the etching hard cover 100. As shown inFIG. 2, the etching hard cover 100 has a square or a rectangular frameshape having an opening corresponding to the pattern region of an EUVphoto mask 5. The etching hard cover 100 is made of a material that canendure the plasma etching of the hard mask layer (Cr contacting layer)30. In some embodiments, the etching hard cover is made of ceramic.Ceramic material includes, for example, but not limited to, boronnitride (BN), alumina (Al₂O₃), silicon nitride (Si₃N₄), silicon carbide(SiC), zirconia (ZrO₂), SiO₂, barium titanate (BaTiO₃), Y₂O₃, PbTiO₃,PbZrO₃, Y₃Al₅O₁₂, YAS (Y₂O₃—Al₂O₃—SiO₂), YF₃, and Y₂O₃—ZrO₂—Al₂O₃. Insome embodiments, the etching hard cover 100 is made of a bulk ceramicmaterial, or a ceramic coated on metal or other material. The ceramicmaterial may be a sintered body. In other embodiments, glass or metallicmaterial coated with a ceramic material can be used for the etching hardcover 100. In some embodiments, the surface of the etching hard cover100 is coated with a coating material such as a silicon oxide, siliconnitride or any other material durable to the etching gas for the lightblocking layer 20. The etching hard cover 100 is attachable to anddetachable from the EUV photo mask 5 to be processed and is reusable.

FIG. 3 shows a schematic view of an etching operation using a hardetching cover according to one embodiment of the present disclosure.FIG. 3 shows the absorber etching operation using the hard mask layer 30as an etching mask, corresponding to FIG. 1D.

As shown in FIG. 3, a plasma etching apparatus includes a stage 200having a capture ring 220 supported by a pedestal 210 and an electricchucking mechanism having a cathode 230 and burls (protrusions) 235disposed thereon. The etching hard cover 100 is supported by the capturering 220 of the stage 200 in some embodiments. Further the EUV photomask 5 is supported by the burls (protrusions) 235 of the cathode 230 ofthe electric chuck mechanism in some embodiments. The stage, thepedestal and the electric chuck mechanism are disposed inside a plasmaetching chamber. The etching hard cover 100 is supported by the capturering 220 such that a main cover portion 101 of the etching hard cover100 covers an edge portion of the surface of the hard mask layer 30 (theedge portion of the EUV photo mask 5). In some embodiments, the maincover portion 101 (a frame portion) of the etching hard cover 100 has athickness T1 in a range from about 0.3 mm to about 0.8 mm. A side frame103 (thick portion) of the etching hard cover 100, which is supported bythe capture ring 220 of the stage 200, may have a thickness T2 in arange from about 0.6 mm to about 1.6 mm in some embodiments.

The space S1 between the lower surface of the main cover portion 101 ofthe etching hard cover 100 and the upper surface of the hard mask layer30 when the etching hard cover 100 is placed on the capture ring 220 isin a range from about 0 mm (touching) to about 1.0 mm in someembodiments. As shown in FIG. 3, the main cover portion 101 overlaps theEUV photo mask 5. When a distance between the edge of the EUV photo mask5 to the edge of the main cover portion 101 is W1 (cover amount), thecover amount W1 is in a range from about 5 mm to about 10 mm. In someembodiments, the cover amount W1 is determined such that the main coverportion 101 does not overlap the region where a back border 51 isformed. Further, in some embodiments, there is a gap or a space betweenthe side face of the EUV photo mask 5 and the side frame 103 of theetching hard cover 100. The amount S2 of the gap is in a range fromabout 1 mm to about 3 mm in some embodiments.

By using the etching hard cover 100, it is possible to prevent activespecies of plasma PL from entering the side portions and the backportion of the EUV photo mask during the plasma etching. Thus, it ispossible to prevent damage on the backside conductive layer 45.

FIG. 4A shows a cross section shape of the etching hard cover 100according to another embodiment of the present disclosure. In thisembodiment, the lower surface of the main cover portion 101 of theetching hard cover 100 includes an abutting portion, for example, aprotrusion 105 that contacts the upper surface of the EUV photo mask 5.The protrusion 105 is a line shape pattern and formed along the entirecircumference of the etching hard cover 100 in some embodiments. Inother embodiments, multiple protrusions 105 are discretely providedalong the circumference of the etching hard cover 100. A protrudingamount of the protrusion 105 is in a range from about 0.1 mm to about1.0 mm in some embodiments. When the protrusion 105 is used, it ispossible to minimize the contact area of the etching hard cover 100 tothe surface of the EUV photo mask 5 when the etching hard cover 100 isin contact with the EUV photo mask 5. In other embodiments, there is agap between the protrusion 105 and the upper surface of the EUV photomask 5. In certain embodiments, the gap is in a range from about 0 mm toabout 0.1 mm.

FIG. 4B shows a cross section shape of the etching hard cover 100according to another embodiment of the present disclosure. In thisembodiment, a protrusion 107 similar to the protrusion 105 of FIG. 4A isformed at the inside surface of the side frame 103, as shown in FIG. 4B.The protrusion 107 is to be in contact with the side face of the EUVphoto mask 5. In some embodiments, the protrusion 107 is in contact withthe side surface of the absorber layer 25. In other embodiments, theprotrusion 107 is in contact with the side surface of one of the cappinglayer 20, the multilayer Mo/Si stack 15 and the substrate 10. Theprotrusion 107 is a line shape pattern and formed along the entirecircumference of the etching hard cover 100 in some embodiments. Inother embodiments, multiple protrusions 107 are discretely providedalong the circumference of the etching hard cover 100. A protrudingamount of the protrusion 107 is in a range from about 0.1 mm to about1.0 mm in some embodiments. In some embodiments, the protrusion 107 isin contact with the side face of the EUV photo mask 5 and in otherembodiments, there is a gap between the protrusion 107 and the uppersurface of the EUV photo mask 5. In certain embodiments, the gap is in arange from about 0 mm to about 0.1 mm.

In some embodiments, both the protrusion 105 and the protrusion 107 areprovided to the etching hard cover 100.

FIG. 4C shows another embodiment of the etching hard cover 100 accordingto the present disclosure. In this embodiment, instead of a protrusion105 shown in FIG. 4A, an O-ring 115 embedded in a groove formed on thelower surface of the main cover portion 101 is used to be in contactwith the upper surface of the EUV photo mask 5. The O-ring 115 is madeof an elastic material, for example, but not limited to, rubber (e.g.,butadiene rubber, butyl rubber, ethylene propylene diene monomer rubber,or nitrile rubber), polytetrafluoroethylene (PTFE), perfluoroelastomer,or silicone. Similar to the line shaped protrusion 105, the use of theO-ring 115 can minimize the contact area of the etching hard cover 100to the surface of the EUV photo mask 5. The diameter of the O-ring is ina range from about 1 mm to 5 mm in some embodiments.

FIG. 4D shows another embodiment of the etching hard cover 100 accordingto the present disclosure. In this embodiment, instead of a protrusion107 shown in FIG. 4B, an O-ring 117 embedded in a groove formed on thelower surface of the main cover portion 101 is used to be in contactwith the upper surface of the EUV photo mask 5. The O-ring 117 is madeof an elastic material, for example, but not limited to, rubber (e.g.,butadiene rubber, butyl rubber, ethylene propylene diene monomer rubber,or nitrile rubber), polytetrafluoroethylene (PTFE), perfluoroelastomer,or silicone. Similar to the line shaped protrusion 105, the use of theO-ring 117 can minimize the contact area of the etching hard cover 100to the surface of the EUV photo mask 5. The diameter of the O-ring is ina range from about 1 mm to 5 mm in some embodiments.

In some embodiments, both the O-ring 115 and the O-ring 117 are providedto the etching hard cover 100. In some embodiments, one of theprotrusions 105 and 107 and one of the O-rings 115 and 117 are combined.

FIG. 4E shows a line-shape protrusion 105 or a line-shaped O-ring 115according to embodiments of the present disclosure. In some embodiments,the shape of the outer peripheral of the etching hard cover 100 is ovalor circular, while the shape of the inner peripheral of the opening issquare or rectangular as shown in FIG. 4F.

FIG. 5 shows operations of loading an EUV photo mask to be etched intoan etching chamber through a load lock chamber. In some embodiments, anEUV photo mask 5 to be subjected to a plasma etching is stored in a SMIF(Standard Mechanical Interface) pod and carried by the SMIF pod to anetching apparatus. The EUV photo mask 5 is transferred from the SMIF podto a load lock chamber of the etching apparatus. In the load lockchamber, the EUV photo mask 5 is placed on a stage 400 in someembodiments. After the EUV photo mask 5 is placed on the stage 400, anetching hard cover 100 is placed on the EUV photo mask 5 from above, asshown in FIG. 5. After the etching hard cover 100 is placed on the EUVphoto mask 5, the EUV photo mask 5 with the etching hard cover 100 istransferred from the load lock chamber to an etching chamber, as shownin FIG. 5. In the etching chamber, the EUV photo mask 5 is placed onburls 235 of a cathode 230 of an electric chuck. When the EUV photo mask5 is moved down from above to the burls 235, a capture ring 220 of thestage 200 comes in contact with the bottom of the side frame 103 of theetching hard cover 100 just before the backside conductive layer 45comes in contact with the burls 235, or at the same time as the backsideconductive layer 45 comes in contact with the burls 235.

After the etching operation is completed, the EUV photo mask 5 with theetching hard cover 100 is transferred from the etching chamber to theload lock chamber. The etching hard cover 100 is detached from the EUVphoto mask 5 in the load lock chamber, and the EUV photo mask 5 isunloaded from the load lock chamber to the SMIF pod to the nextoperation, such as cleaning.

In other embodiments, the etching hard cover 100 is placed over the EUVphoto mask 5 in the etching chamber. In some embodiments, a coversupporter which can move the etching hard cover 100 up and down isdisposed inside the etching chamber prior to or after a plasma etchingoperation.

FIGS. 9A-9C show view of carious cover support 110 according toembodiments of the present disclosure. In FIG. 9A, one or more supportposts 110 are attached to the bottom of the etching hard cover 100. Thesupport posts 110 are coupled to a moving mechanism to move the supportposts 110 vertically relative to the capture ring 220. In FIG. 9B, oneor more support posts 111 are attached to the upper surface of theetching hard cover 100. The support posts 111 are coupled to a movingmechanism to move the support posts 110 vertically relative to thecapture ring 220. Further, in FIG. 9C, one or more support posts 112laterally extend from the etching hard cover 100. The support posts 110are coupled to a moving mechanism to move the support posts 110vertically relative to the capture ring 220.

In the foregoing embodiments, the etching hard cover 100 is used in anetching operation to etch the absorber layer 25 by using the hard masklayer 30 as an etching mask. The etching hard cover 100 can also be usedin an etching of the hard mask layer 30 by using the first photo resistlayer 35 as an etching mask, as shown in FIG. 1B. In such a case, thebottom of the main cover portion 101 of the etching hard cover 100 (orthe protrusion 105 or the O-ring 115) may be in contact with the firstphoto resist layer 35.

The etching hard cover 100 can also be used in an etching of theabsorber layer 25, the capping layer 20, and the multilayer Mo/Si stack15 by using the second photo resist layer 45 as an etching mask, asshown in FIG. 1F. In such a case, the bottom of the main cover portion101 of the etching hard cover 100 (or the protrusion 105 or the O-ring115) may be in contact with the second photo resist layer 45.

FIG. 6 shows a schematic view of an etching operation of an EUV photomask according to one embodiment of the present disclosure, to preventthe active species of the plasma from entering the bottom portion of theEUV photo mask during plasma etching.

In some embodiments, the stage 200 of the etching apparatus isconfigured such that when an EUV photo mask 5 is placed on the burls 235of the cathode 230 of the electric chuck, the bottom surface of thesubstrate 10 is in contact with a flat portion 222 of the capture ring220, as shown in FIG. 6. In some embodiments, a difference D1 in heightbetween the flat portion 222 and the burl 235 is substantially equal tothe thickness of the backside conductive layer 45 and is in a range fromabout 10 nm to about 100 nm. In some embodiments, there is a small gapbetween the bottom surface of the substrate 10 and the flat portion 222.In certain embodiments, the gap is in a range from about 0 mm to about0.1 mm.

According to this configuration, it is possible to prevent activespecies of plasma PL from entering the back portion of the EUV photomask 5 during the plasma etching. Thus, it is possible to prevent damageon the backside conductive layer 45. In this configuration, an etchinghard mask cover 100 may or may not be used.

FIG. 7 shows a schematic view of an etching operation of an EUV photomask according to one embodiment of the present disclosure, to preventthe active species of the plasma from entering the bottom portion of theEUV photo mask during plasma etching.

In some embodiments, the flat portion 225 of the capture ring 220 of thestage 200 has a protrusion 225, such that when an EUV photo mask 5 isplaced on the burls 235 of the cathode 230 of the electric chuck, thebottom surface of the substrate 10 is in contact with the protrusion 225of the capture ring 220, as shown in FIG. 7. In some embodiments, thereis a small gap between the bottom surface of the substrate 10 and theprotrusion 225. In certain embodiments, the gap is in a range from about0 mm to about 0.1 mm.

The protrusion 225 is a line shape pattern and formed along the entirecircumference of the flat portion 222 in some embodiments. In otherembodiments, multiple protrusions 225 are discretely provided along thecircumference of the flat portion 222. A protruding amount of theprotrusion 225 is in a range from about 0.1 mm to about 1.0 mm in someembodiments. When the protrusion 225 is used, it is possible to minimizethe contact area of the flat portion 222 of the capture ring 220 to thebottom surface of the substrate 10 of the EUV photo mask 5 when thesubstrate 10 of the EUV photo mask 5 is in contact with the flat portion222. In other embodiments, there is a gap between the protrusion 225 andthe bottom surface of the substrate 10 of the EUV photo mask 5. Incertain embodiments, the gap is in a range from about 0 mm to about 0.1mm. By using the protrusion 225 on the flat portion 222 of the stage200, it is possible to prevent active species of plasma PL from enteringthe back portion of the EUV photo mask 5 during the plasma etching.Thus, it is possible to prevent damage on the backside conductive layer45. In this configuration, an etching hard mask cover 100 may or may notbe used.

FIG. 8 shows a schematic view of an etching operation of an EUV photomask according to one embodiment of the present disclosure, to preventthe active species of the plasma from entering the bottom portion of theEUV photo mask during plasma etching.

In this embodiment, instead of a protrusion 225 shown in FIG. 7, anO-ring 227 embedded in a groove formed on the flat portion 222 of thecapture ring 220 of the stage 200 is used to be in contact with thebottom surface of the substrate 10 of the EUV photo mask 5. The O-ring227 is made of an elastic material, for example, but not limited to,rubber (e.g., butadiene rubber, butyl rubber, ethylene propylene dienemonomer rubber, or nitrile rubber), polytetrafluoroethylene (PTFE),perfluoroelastomer, or silicone. Similar to the line shaped protrusion225, the use of the O-ring 227 can minimize the contact area of the flatportion 222 of the stage 200 to the bottom surface of the substrate 10of the EUV photo mask 5. The diameter of the O-ring is in a range fromabout 1 mm to 5 mm in some embodiments. By using the O-ring 227 on theflat portion 222 of the stage 200, it is possible to prevent activespecies of plasma PL from entering the back portion of the EUV photomask 5 during the plasma etching. Thus, it is possible to prevent damageon the backside conductive layer 45. In this configuration, an etchinghard mask cover 100 may or may not be used.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

For example, by using a detachable etching hard cover in the etchingoperation for an EUV photo mask 5 having a backside conductive layer tocover the edge portion of the EUV photo mask, it is possible to preventactive species of plasma from entering the side portions and the backportion of the EUV photo mask during the plasma etching. Thus, it ispossible to prevent damage on the backside conductive layer 45 and toprevent generation of particles or unsecure chucking to the electricsubstrate chucking mechanism. Further, by contacting the bottom surfaceof the substrate to the flat portion of the capture ring of the stage200, it is possible to prevent active species of plasma from enteringthe back portion of the EUV photo mask during the plasma etching. Thus,it is possible to prevent damage on the backside conductive layer 45 andto prevent generation of particles or unsecure chucking to the electricsubstrate chucking mechanism.

In accordance with one aspect of the present disclosure, in a method ofmanufacturing a photo mask, an etching mask layer having circuitpatterns is formed over a target layer of the photo mask to be etched.The photo mask includes a backside conductive layer. The target layer isetched by plasma etching, while preventing active species of plasma fromattacking the backside conductive layer. In one or more of the foregoingand following embodiment, an edge portion of the target layer is coveredwith an etching hard cover, while a region of the target layer to beetched is exposed through an opening of the etching hard cover. In oneor more of the foregoing and following embodiment, the etching hardcover is reusable. In one or more of the foregoing and followingembodiment, the etching hard cover is made of ceramic. In one or more ofthe foregoing and following embodiment, the etching hard cover has aframe shape having the opening and a frame portion defining the openingand a side frame from which the frame portion extends. In one or more ofthe foregoing and following embodiment, the frame portion covers theedge portion. In one or more of the foregoing and following embodiment,a bottom surface of the frame portion is in contact with the etchingmask layer. In one or more of the foregoing and following embodiment, abottom surface of the frame portion is not in contact with the etchingmask layer with a gap. In one or more of the foregoing and followingembodiment, the gap is equal to or less than 1 mm. In one or more of theforegoing and following embodiment, a bottom surface of the frameportion includes a protrusion. In one or more of the foregoing andfollowing embodiment, the protrusion is a line shape. In one or more ofthe foregoing and following embodiment, the protrusion is in contactwith the etching mask layer. In one or more of the foregoing andfollowing embodiment, the side frame includes a protrusion. In one ormore of the foregoing and following embodiment, the protrusion is a lineshape. In one or more of the foregoing and following embodiment, theprotrusion is in contact with side surfaces of the photo mask. In one ormore of the foregoing and following embodiment, a bottom surface of theframe portion includes a groove in which an O-ring is disposed. In oneor more of the foregoing and following embodiment, the O-ring is incontact with the etching mask layer. In one or more of the foregoing andfollowing embodiment, the side frame includes a groove in which anO-ring is disposed. In one or more of the foregoing and followingembodiment, the O-ring is in contact with side surfaces of the photomask. In one or more of the foregoing and following embodiment, thephoto mask is placed on a stage such that a bottom surface of the photomask where no backside conductive layer is disposed is in contact withthe stage. In one or more of the foregoing and following embodiment, thebackside conductive layer is in contact with an electric chuck and isnot in contact with the stage. In one or more of the foregoing andfollowing embodiment, the stage includes a protrusion in contact withthe bottom surface of the photo mask. In one or more of the foregoingand following embodiment, the stage includes a groove in which an O-ringin contact with the bottom surface of the photo mask is disposed. In oneor more of the foregoing and following embodiment, the photo mask isplaced on a stage such that a bottom surface of the photo mask where nobackside conductive layer is disposed is placed above the stage with agap equal to or less than 0.5 mm.

In accordance with another aspect of the present disclosure, an etchinghard cover for an EUV photo mask manufacturing operation is made ofceramic. The etching hard cover has a frame shape having an opening anda frame portion defining the opening and a side frame from which theframe portion extends, and at least one of a bottom surface of the frameportion and the side frame includes an abutting portion configured toabut the photo mask, when the etching hard cover is placed over thephoto mask. In one or more of the foregoing and following embodiment,the bottom surface of the frame portion includes a protrusion as theabutting portion. In one or more of the foregoing and followingembodiment, the protrusion is a line shape. In one or more of theforegoing and following embodiment, the side frame includes a protrusionas the abutting portion. In one or more of the foregoing and followingembodiment, the protrusion is a line shape. In one or more of theforegoing and following embodiment, the bottom surface of the frameportion includes a groove in which an O-ring is disposed. In one or moreof the foregoing and following embodiment, the side frame includes agroove in which an O-ring is disposed.

In accordance with another aspect of the present disclosure, an etchingapparatus for etching a target layer of a photo mask includes a maskstage and an electric chuck to hold the photo mask. The mask stageincludes a protrusion at a flat surface of the mask stage to be incontact with a bottom surface of the photo mask. In accordance withanother aspect of the present disclosure, an etching apparatus foretching a target layer of a photo mask includes a mask stage and anelectric chuck to hold the photo mask. The mask cover includes a groovein which an O-ring to be in contact with a bottom surface of the photomask is disposed.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of manufacturing a photo mask, themethod comprising: forming an etching mask layer having circuit patternsover a target layer of the photo mask to be etched, the photo maskincluding a backside conductive layer; covering an edge portion of thetarget layer with an etching hard cover, while a region of the targetlayer to be etched is exposed through an opening of the etching hardcover; and etching the target layer by plasma etching through theopening, while preventing active species of plasma from attacking thebackside conductive layer.
 2. The method of claim 1, wherein the etchinghard cover is reusable.
 3. The method of claim 1, wherein the etchinghard cover is made of ceramic.
 4. The method of claim 1, wherein theetching hard cover has a frame shape having the opening and a frameportion defining the opening and a side frame from which the frameportion extends.
 5. The method of claim 4, wherein the frame portioncovers the edge portion.
 6. The method of claim 4, wherein a bottomsurface of the frame portion is in contact with the etching mask layer.7. The method of claim 4, wherein a bottom surface of the frame portionis not in contact with the etching mask layer with a gap.
 8. The methodof claim 7, wherein the gap is equal to or less than 1 mm.
 9. The methodof claim 4, wherein a bottom surface of the frame portion includes aprotrusion.
 10. The method of claim 9, wherein the protrusion is a lineshape.
 11. The method of claim 9, wherein the protrusion is in contactwith the etching mask layer.
 12. A method of manufacturing a photo mask,comprising: forming an etching mask layer having circuit patterns over atarget layer of the photo mask to be etched, the photo mask including abackside conductive layer; placing the photo mask on a stage in anetching apparatus; and etching the target layer by plasma etching in theetching apparatus, wherein: the stage comprises a capture ring and anelectric chuck mechanism including a cathode, and the photo mask isplaced on the stage such that a bottom surface of the photo mask whereno backside conductive layer is disposed is placed above the capturering, and the backside conductive layer is placed on the cathode. 13.The method of claim 12, wherein the bottom surface of the photo maskwhere no backside conductive layer is disposed is in contact with thecapture ring.
 14. The method of claim 13, wherein the capture ringincludes a protrusion in contact with the bottom surface of the photomask where no backside conductive layer is disposed.
 15. The method ofclaim 13, wherein the capture ring includes a groove in which an O-ringin contact with the bottom surface of the photo mask where no backsideconductive layer is disposed is disposed.
 16. The method of claim 12,wherein the bottom surface of the photo mask where no backsideconductive layer is disposed is not in contact with the capture ring.17. The method of claim 12, wherein the backside conductive layer is notin contact with the capture ring.
 18. The method of claim 17, wherein agap between the bottom surface of the photo mask where no backsideconductive layer is disposed and the capture ring is equal to or lessthan 0.2 mm.
 19. An etching apparatus for etching a target layer of aphoto mask, comprising: a mask stage; and an electric chuck to hold thephoto mask, wherein: the mask stage includes a capture ring and anelectric chuck mechanism including a cathode, the capture ringsurrounding the electric chuck, a first protrusion is provided at a flatsurface of the capture ring of the mask stage, a second protrusion isprovided on the cathode, and the electric chuck is configured to move upand down relative to the capture ring.
 20. The etching apparatus ofclaim 19, wherein the first protrusion is an O-ring disposed in a grooveformed in the capture ring.